package com.company.netease2018;

import java.util.*;

public class first {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String line = sc.next();
        char[] chars = line.toCharArray();
        Set<Character> set = new HashSet<>();
        for(char item: chars){
            set.add(item);
        }
        double avg = ((double)line.length()) / set.size();
        int res = (int)((avg + 0.005) * 100);
        System.out.println(((double) res)/100);
    }


}
